The present invention relates to methods for forming wiring structures in electronic devices such as semiconductor devices.
Examples of known methods for forming wiring structures include a prior art (see, for example, Japanese Laid-Open Publication No. 11-186261) in which heat treatment (hereinafter, referred to as annealing) is performed after a chemical mechanical polishing (CMP) process. Hereinafter, the prior art method for forming a wiring structure will be described with reference to the drawings with the case where wire is formed in a wiring groove formed in an insulating film taken an example.
FIGS. 13A through 13E are cross-sectional views showing respective process steps of a method for forming a wiring structure according to the prior art.
First, as shown in FIG. 13A, an underlying oxide film 12 is deposited by a plasma CVD (chemical vapor deposition) process over a silicon substrate 11, and then a SiN film 13 and a SiO2 film 14 are deposited in this order with similar processes. Subsequently, the SiO2 film 14 is etched using a resist pattern (not shown) as a mask, thereby forming a recess reaching the SiN film 13. Thereafter, the resist pattern and the exposed part of the SiN film 13 are removed, thereby forming a wiring groove 15.
Next, as shown in FIG. 13B, a barrier metal TaN film 16 is deposited by a sputtering process over the SiO2 film 14 provided with the wiring groove 15, and then a Cu seed film 17 is deposited over the barrier metal TaN film 16.
Thereafter, as shown in FIG. 13C, a Cu plating layer 18 is deposited by an electrolytic plating process over the SiO2 film 14 to fill the wiring groove 15 completely.
Subsequently, as shown in FIG. 13D, respective parts of the Cu plating layer 18, Cu seed film 17 and barrier metal TaN film 16 located outside the wiring groove 15 are removed by a CMP process, thereby exposing the surface of the SiO2 film 14. In this manner, a Cu buried wiring layer 19 is formed in the wiring groove 15.
Then, an annealing process is performed at a temperature of 300 to 500xc2x0 C. for a holding time of 5 to 2000 seconds, thereby eliminating, for example, moisture, hydrogen and carbon dioxide contained in the Cu buried wiring layer 19 as well as increasing the grain size of the Cu buried wiring layer 19, as shown in FIG. 13E.
Through the foregoing process steps, a copper wire for a semiconductor device is formed.
However, the prior art has a problem described later.
FIG. 14 is a view for explaining the problem in the prior art.
As shown in FIG. 14, a SiN film 43, a SiO2 film 44 and a FSG film (fluorine-doped silicon oxide film) 45 are formed in this order over an insulating film 41 in which a lower wiring layer 42 is buried. The SiN film 43, the SiO2 film 44 and the FSG film 45 are provided with a recess 46 and a wiring groove 47. More specifically, the recess 46 is made up of: a via hole 46a formed through the SiN film 43 and the SiO2 film 44 to reach the lower wiring layer 42; and a wiring groove 46b formed in the FSG film 45 and connected to the via hole 46a. The wiring groove 47 is also formed in the FSG film 45 in the same manner as the wiring groove 46b. The recess 46 and the wiring groove 47 are filled with a copper film (a conducive film for upper wiring) 49 that is surrounded by a barrier film 48. A SiN film 50 is formed on the FSG film 45 and the copper film 49.
In the prior art, however, if the copper film 49 is annealed after a CMP process (see FIG. 13D) in a process for forming wiring, there arises a problem that surface defects such as a surface fracture 51 and a crack 52 are created in the surface of the copper film 49 buried in, for example, the recess 46, as shown in FIG. 14.
It is therefore an object of the present invention to provide a method for preventing the occurrence of surface defects in a conductive film for wiring and thus fabricating an electronic device such as a semiconductor device with a highly-reliable wiring structure with a good yield.
In order to achieve this object, the present inventor has studied causes of the surface fracture 51 and the crack 52 occurring in the prior art in which xe2x80x9cannealingxe2x80x9d is performed xe2x80x9cafter a CMP processxe2x80x9d to obtain the following findings. That is to say, in the prior art, the copper film 49 buried in, for example, the recess 46 is annealed so that the crystallization of the copper film 49 is completed. Accordingly, defects (e.g., vacancies at the atomic level existing along a grain boundary) contained in the copper film 49 gather in the surface of the copper film 49, which has been already planarized, and in addition, the copper film 49 shrinks unevenly. As a result, the surface fracture 51 and the crack 52 occur as shown in FIG. 14. Although the SiN film 50 is deposited over the entire surface of the wiring structure including the copper film 49 after the formation of the structure in the prior art, the surface fracture 51 and the crack 52 are not filled with the SiN film 50 because the SiN film 50 has a low step coverage. Therefore, the surface defects such as the surface fracture 51 created in the surface of the copper film 49 to serve as wiring are left without being treated. As a result, these surface defects act as paths for surface diffusion of copper atoms, thus greatly deteriorating resistance to electromigration.
In view of this, the present inventor has come up with a method for forming a highly-reliable wiring structure by performing xe2x80x9cCMP processesxe2x80x9d separately xe2x80x9cbefore and after an annealing processxe2x80x9d in order to simultaneously remove the surface defects created in a conductive film for wiring during the annealing process and a surface portion of the conductive film for wiring.
Specifically, an inventive method for forming a wiring structure includes the steps of: forming a recess in an insulating film; depositing a conductive film over the insulating film such that the recess is filled with the conductive film; performing a heat treatment on the conductive film; partly removing the conductive film before the step of performing the heat treatment is performed; and partly removing the conductive film after the step of performing the heat treatment has been performed.
With the inventive method for forming a wiring structure, after a conductive film has been deposited to fill a recess provided in an insulating film, the conductive film is subjected to a heat treatment, and then the conductive film is partly removed before and after the heat treatment. That is to say, the conductive film is partly removed before a heat treatment and the remaining conductive film is subjected to the heat treatment, thereby retaining the hardness of the conductive film such that the conductive film is removed relatively evenly in a removing step after the heat treatment. In addition, the conductive film is also partially removed after the heat treatment, thereby simultaneously eliminating defects such as a surface fracture or crack created in the conduction film during the heat treatment. Accordingly, no path for surface diffusion of atoms constituting the conductive film is created, thus preventing deterioration of the electromigration resistance of the wiring structure. As a result, an electronic device such as a semiconductor device with a highly-reliable wiring structure can be fabricated with a good yield.
In the inventive method for forming a wiring structure, the step of removing the conductive film partly (e.g., a CMP process) performed after the heat treatment allows surface defects such as a fracture created in the conductive film to be removed at a time. In other words, it is possible to remove the surface defects without specially setting conditions for the heat treatment, thus forming a highly-reliable wiring structure without increasing the number of process steps.
The inventive method for forming a wiring structure may include the step of depositing a barrier film over the insulating film so that the recess is halfway filled with the barrier film, before the step of depositing the conductive film is performed, wherein the step of partly removing the conductive film before the step of performing the heat treatment may include the step of removing part of the conductive film located outside the recess, thereby exposing part of the barrier film located outside the recess, and the step of partly removing the conductive film after the step of performing the heat treatment may include the step of removing the part of the barrier film located outside the recess and a surface portion of the remaining conductive film.
Then, more suitable conditions for films to be polished can be selected in respective removing steps, e.g., conditions suitable for polishing the conductive film are selected in the removing step before the heat treatment whereas conditions suitable for polishing the barrier film are selected in the removing step after the heat treatment. Accordingly, insufficient polishing or excessive polishing is less liable to occur. As a result, polishing can be performed with higher accuracy and a margin required for polishing can be reduced, thereby enabling a flexible process design.
In such a case, if the conductive film is made of copper or an alloy containing copper and the barrier film is made of Ta or TaN, then highly-reliable buried copper wiring is achieved.
The inventive method for forming a wiring structure may include the step of depositing a barrier film over the insulating film so that the recess is halfway filled with the barrier film, before the step of depositing the conductive film is performed, wherein the step of partly removing the conductive film before the step of performing the heat treatment may include the step of partially removing part of the conductive film located outside the recess, and the step of partly removing the conductive film after the step of performing the heat treatment may include the step of removing the part of the conductive film remaining outside the recess and part of the barrier film located outside the recess.
Then, even if a surface fracture or a crack is enlarged resulting from film properties of the conductive film, the surface of the conductive film can be further planarized because the amount of removal of the conductive film is set large in the removing step after the heat treatment.
In such a case, if the conductive film is made of copper or an alloy containing copper and the barrier film is made of Ta or TaN, then highly-reliable buried copper wiring is achieved.
The inventive method for forming a wiring structure may include the step of depositing a barrier film over the insulating film so that the recess is halfway filled with the barrier film, before the step of depositing the conductive film is performed, wherein the step of partly removing the conductive film before the step of performing the heat treatment may include the step of removing part of the conductive film located outside the recess and part of the barrier film located outside the recess, and the step of partly removing the conductive film after the step of performing the heat treatment may include the step of removing a surface portion of the remaining conductive film.
Then, in the removing step after the heat treatment (i.e., the step of removing a surface portion of the remaining conductive film), even if conditions suitable for removing an insulating film such as an oxide film is selected, other than the conditions suitable for removing the conductive film and the conditions suitable for removing the barrier film, it is possible to obtain the effect of smoothing the surface of the conductive film. Specifically, in the case where an oxide film around the wiring is removed by CMP using conditions suitable for removing an oxide film, a strong force is also applied to the conductive film for wiring, so that the surface of the conductive film is planarized simultaneously with the removal of the oxide film.
In such a case, if the conductive film is made of copper or an alloy containing copper and the barrier film is made of Ta or TaN, then highly-reliable buried copper wiring is achieved.
In the inventive method for forming a wiring structure, the recess may include: a via hole; and a wiring groove formed on the via hole and connected to the via hole. Then, a highly-reliable wiring structure having a dual damascene structure is achieved.
In the inventive method for forming a wiring structure, the heat treatment is preferably performed at a temperature higher than or equal to 200xc2x0 C. and less than 500xc2x0 C.
Then, the crystal of the conductive film is fully grown inside the recess, thereby densifying the conductive film. Accordingly, in a heat treatment performed after the formation of the wiring structure, further crystal growth of the conductive film does not occur inside the recess, thus preventing the shrinkage of the conductive film and the occurrence of, for example, a surface fracture due to the shrinkage.
In the inventive method for forming a wiring structure, if the recess has a width of 0.25 xcexcm or less, the above-described advantages are remarkably exhibited.
In the inventive method for forming a wiring structure, if the conductive film is made of copper or an alloy containing copper, highly-reliable buried copper wiring is achieved.
In the inventive method for forming a wiring structure, if in the steps of partly removing the conductive film, a chemical mechanical polishing process is used, part of the conductive film outside the recess can be removed as intended.
An inventive method for fabricating an electronic device is predicated upon a method for fabricating an electronic device including a first wiring structure and a second wiring structure. Specifically, a method for forming the first wiring structure includes the steps of: forming a first recess in a first insulating film; depositing a first conductive film over the first insulating film such that the first recess is filled with the first conductive film; performing a heat treatment on the first conductive film; partly removing the first conductive film before the step of performing the heat treatment is performed; and partly removing the first conductive film after the step of performing the heat treatment has been performed. A method for forming the second wiring structure includes the steps of: forming a second recess in a second insulating film; depositing a second conductive film over the second insulating film such that the second recess is filled with the second conductive film; performing a heat treatment on the second conductive film; and removing part of the second conductive film located outside the second recess. In the inventive method for fabricating an electronic device, the second recess has a width greater than the first recess. In the method for fabricating the second wiring structure, part of the second conductive film located outside the second recess may be removed before or after the heat treatment performed on the second conductive film.
With the inventive method for fabricating an electronic device, the inventive method for forming a wiring structure is used to form a first wiring structure in a first recess with a relatively small width of 0.25 xcexcm or less, for example, and therefore the above-described advantages of the method are also obtained. On the other hand, to form a second wiring structure in a second recess with a relatively large width greater than 0.25 xcexcm, for example, xe2x80x9ca CMP processxe2x80x9d is performed only one time xe2x80x9cbefore annealingxe2x80x9d or xe2x80x9cafter annealingxe2x80x9d, considering that defects are easily released from part of the conductive film inside the wide recess. Accordingly, it is possible to achieve a wiring structure without any surface defect such as a surface fracture, while suppressing the complication of the process.
That is to say, with the inventive method for fabricating an electronic device, the timing of and the number of a CMP process for forming a wiring structure are selectively set in accordance with the width of the recess, i.e., the wiring width, so that it is possible to form a desired wiring structure, without complicating the process excessively.